In a vehicle, various electronic components and devices, such as illuminated key entry system, defogger timer, seat belt warning system, light turning-off reminding warning system, key takeout reminding warning system, power door lock, and keyless entry system, are independently installed and distributed. These electronic components are electrically connected with a meter unit mounted in front of the driver's seat. The electronic components are controlled by system means such as a microcomputer incorporated in the meter unit in accordance with a program previously stored in a ROM of the meter unit. The state of the vehicle detected by the electronic components is displayed on the meter unit if necessary (for example, see Japanese Unexamined Patent Publication No. 203553/1995.)
Integration of the distributed independent electronic components is considered as means for achieving cost reduction. The combination of the required electronic components differs according to the vehicular specifications for specific climatic areas or the vehicle grade. Therefore, if electronic components are integrated simply according to the combination, then the number of variations increases. Consequently, large cost reduction cannot be expected.
Japanese Unexamined Patent Publication No. 276571/1994 discloses a multiplexed transmission device for a vehicular electric system. This multiplexed transmission device is separate from electronic components, unlike the prior art device. Since these two kinds of systems can be separately developed and manufactured, it is possible to prevent the electronic components and the multiplexed transmission device from increasing in total number. Even with this structure, however, the number of variations described above cannot be sufficiently decreased.